1. Field of the Invention
This invention relates to improvements in a solenoid valve adapted to make an open-and-close control of an oil passage or the like, and more particularly to the structure of a plunger of the solenoid valve to securely keeping a spherical valve member at its tip end.
2. Description of the Prior Art
As is well known, a plurality of solenoid valves of normally closed or opened types are provided in a fluid circuit, for example, of an anti-lock braking system for an automotive vehicle. A typical one of these solenoid valves is disclosed in Japanese Patent Publication No. 3-49781 and shown in FIG. 6 in the drawings of the present application.
In FIG. 6, a valve body 1 is formed thereinside a plurality of oil passages 2a, 2b. A solenoid coil 3 forming part of a solenoid valve V is disposed in the valve body 1. A cylindrical armature core 4 is disposed inside the inner peripheral portion of the solenoid coil 3. A movable plunger 5 is disposed inside the cylindrical armature core 4 and slidably movable in the axial direction of the cylindrical armature core 4. The plunger 5 is formed of a magnetic material which is relatively low in hardness or rigidity. The plunger 5 is generally cylindrical to form an axially extending central hole 5a in which a pair of valve members 6, 7 are press-fitted and fixed. The valve members 6, 7 are generally rod-like and have a circular cross-section, and located spaced and opposite to each other. The valve members 6, 7 respectively project from the opposite ends of the cylindrical armature 5. The valve members 6, 7 are respectively seatable on valve seats 9, 10 which are respectively formed with passage holes 8a, 8b. The passage holes 8a, 8b are respectively in communication with the oil passages 2a, 2b.
When the armature core 4 is energized or de-energized upon current supply or interruption to the solenoid coil 3, the plunger 5 moves axially leftward or rightward so that the tip end portion 6a, 7a of each valve member 6, 7 is seated on or separated from each valve seat 9, 10, thus making an open-and-close control of the passage openings 8a, 8b.
However, drawbacks have been encountered in the above conventional solenoid valve V, in which the valve members 6, 7 are press-fitted in the central hole 5a of the plunger 5 low in rigidity and therefore there is the possibility of the plunger 5 being cracked or broken down under an excessive load stress applied to the inner peripheral surface of the plunger 5 particularly in case that a press-fitting force is high or a press-fitting area of each valve member to the plunger is relatively small.
In view of this, it may be proposed that the plunger 5 is formed by machining a metal material high in rigidity in order to prevent the plunger from being damaged. However, if the plunger 5 is formed of the high rigidity metal material, a necessary magnetic characteristics amount not be obtained thereby not only lowering a movement response of the plunger but also inviting a degraded operational efficiency in production and a raised production cost. Additionally, the outer peripheral surface of the valve members 6, 7 is required to be machined at a high accuracy in order to obtain a suitable press-fitting force. Furthermore, the tip end portion 6a, 7a of the frustoconical shape is required to be machined at a high accuracy to obtain a sufficient tight fit with the valve seat 9, 10. Also from this view point, the conventional solenoid valve V is degraded in operational efficiency in production and is unavoidably raised in production cost.